Electrocardiogram (ECG)

Fig 34 ECG machine
An ECG is a medical test that measures the electrical activity of the heart. It is a non-invasive and painless procedure that is performed by attaching electrodes to the skin of the chest, arms, and legs. The electrodes detect the electrical impulses that are generated by the heart and transmit them to a machine, which records the activity as a series of waves on a graph. The resulting graph is called an electrocardiogram, and it provides important information about the heart’s rate, rhythm, and function. ECGs are commonly used to diagnose heart conditions such as arrhythmias, heart attacks, and heart failure.
Fig 33 ECG rhythm

While electrocardiograms (ECGs) are a useful tool in diagnosing heart conditions, there are some limitations and shortfalls to be aware of:

heart rate

ECGs are a snapshot in time

An ECG provides information about the heart's electrical activity at the time it was taken. It does not provide information about the heart's activity before or after the recording. Therefore, if a heart condition is intermittent, an ECG taken during a period of normal activity may not show any abnormalities.


False positives and false negatives

ECGs can sometimes produce false positives or false negatives. False positives occur when an ECG shows abnormalities that are not actually present, while false negatives occur when an ECG fails to detect a heart condition that is present.


Limited Information

An ECG provides information about the heart's electrical activity, but it does not provide information about the heart's structure or function. To get a more complete picture of the heart's health, other tests such as echocardiography, cardiac MRI, or stress tests may be necessary.



The quality of an ECG can depend on the skill and experience of the technician performing the test and the physician reading it, as well as the positioning of the electrodes and the patient's body.

heart rate

Not suitable for all heart conditions

While ECGs are useful for diagnosing certain heart conditions, they may not be helpful in diagnosing others. For example, an ECG may not be able to detect a chronic blockage in a coronary artery, which is often diagnosed through other imaging tests.

It’s important to note that while ECGs have their limitations, they are still an important tool in diagnosing and monitoring heart conditions. However, they should be interpreted in conjunction with other diagnostic tests and a patient’s clinical history. If you have an ECG that was done at the time of an arrhythmia, its important to bring it with you when you see your electrophysiologist as it will help in making the diagnosis.